An electrosurgical tool system, often referred to as an electrosurgical system, is a set of components used to flow current through a patient to accomplish a specific medical procedure. Often the procedure is to ablate at least some of the tissue through which the current is flowed to accomplish a desirable therapeutic effect. For example, an electrosurgical procedure is sometimes performed to selectively remove nerve tissue. This may be desirable if a set of the patient's nerves continually transmit signals to the brain that inaccurately indicate that a portion of the patient's body is in appreciable pain. If the receipt of these pain signals adversely affects the quality of life for the patient, an electrosurgical system is employed to ablate the nerves responsible for the transmission of these signals. As a consequence of the tissue ablation process the nerve becomes a lesion. As a result of the nerve becoming a lesion, the nerve no longer transmits pain signals to the brain.
Many electrosurgical systems include a cannula and electrode assembly. As implied by its name this assembly includes a cannula and an electrode. The cannula is a needle like structure with sufficient strength to puncture the skin of the patient and be positioned adjacent the tissue through which the current is to be flowed. The distal end or tip of the cannula is conductive. The electrode is a closed end tube formed of conductive material. The tube is designed to seat in the lumen that extends through the cannula. Owing to the relatively small diameter of the electrode, often 0.4 mm or less in diameter, this tube tends to be relatively fragile. A hub or terminal is connected to the proximal end of the electrode body.
When this type of assembly is used to remove tissue, the cannula is typically initially inserted into the patient and directed to a location adjacent the target tissue, the tissue that is to be removed. During the insertion process a stylet may be seated in the cannula lumen to provide structural strength to the cannula. Once the cannula is in the generally vicinity of the target tissue, the stylet is removed. The electrode is inserted into the cannula lumen. A cable connects the electrode to a control console, also part of the electrosurgical system. The control console functions as the power source that applies current to the electrode. An electrically conductive ground pad, another component of the electrosurgical system, is placed against the patient. The ground pad is also connected to the control console.
The electrode assembly is used by sourcing a current from the control console to the electrode. Since the electrode and cannula physically abut, there is current flow to the cannula. An electrical path is established through the patient from the electrode and sleeve section of the cannula to the ground pad. This current flow is densest through the tissue immediately adjacent the distal end of electrode and the exposed distal end of the cannula. This current flow heats the tissue to a temperature that results in the ablation of the tissue.
Available cannula and electrode assemblies have proven to be good instruments for removing selected sections of tissue. Nevertheless, a limiting characteristic with the use of some of these assemblies is that, when activated, they tend to ablate relatively small volumes of tissue, tissue having a volume of 0.8 cm3 or less. This is especially true of assemblies having cannula with outer diameters of 18 gage or more (1.25 mm or less.) There are procedures in which the practitioner wants to ablate larger sections of tissue than can be removed in a single actuation of the assemblies. Consequently, after a first section of tissue is removed, the practitioner has to reposition the electrode assembly to remove an adjacent section of tissue. This requires the practitioner to, ever so slightly, reposition the electrode array so that, in the next actuation, current is only flowed through the tissue that is to be removed and not flowed through the adjacent tissue that should not be subjected to the removal process. Having to so reposition the electrode assembly, in addition to requiring a significant amount of skill, can lengthen the overall amount of time it takes to perform the procedure.
An alternative cannula-and-electrode assembly has been proposed that is intended to increase the volume of tissue that can be removed with a single placement of the cannula. Specifically, it has been proposed to form the cannula of this type of assembly with a side opening that is located a short distance rearward of the distal end of the cannula. The assembly is further constructed with a means to turn the electrode as it is inserted in the cannula so that the distal end tip of the electrode extends out of this side port. The assembly thus has two tips: the distal end tip of the cannula; and the distal end tip of the electrode. When current is sourced to the assembly, the current flows from these two spaced apart tips.
Consequently, when current is sourced out of the electrode assembly of this invention, a relative dense electric field appears in the area around both of the tips. The field extend over a wider volume than the field output by an assembly with a convention electrode-in-the distal end of the cannula construction. The electrode assembly of this invention thus outputs a relatively dense current flow through a volume larger than is output by a conventionally constructed electrode assembly of the same size.
There are procedures though in which the practitioner may not know until after the procedure is started if it is more appropriate to source current through a one tip assembly or a two tip assembly. Similarly, during the procedure, the practitioner may want to initial apply current using first the one tip (or two tip) assembly and then switch to applying current using a two tip (or one tip) assembly. In either of the above situations, the practitioner may find it necessary to interrupt the procedure in order first remove one cathode and electrode assembly and then insert a second assembly. As part of this process, the practitioner needs to take the time to ensure that the second assembly is properly positioned. Having to perform all these steps can increase the complexity of the procedure and the tip it takes to perform the procedure.